View Full Version : Battery not charging with new alternator?


Andelin74
02-14-2011, 06:35:46 PM
Ok so here's the story: My battery has been dying a bunch these past few weeks, so i tested the alternator and it wasn't giving a charge, I assumed the alternator was bad and put a brand new one on.

Now i hooked up the voltage tester to the battery with the new alternator and the car still seems to be running off just the battery (at about 12 volts). So, like anyone else, i assumed it was an issue with wiring, maybe an old wire had stopped working or something, so to make sure I ran a wire straight from the BAT terminal on the alternator to the positive battery post.

STILL no charging, does this mean it's an issue with the battery? I've been charging it with an external charger without any problems at all, so i don't see why it wouldn't take a charge from an alternator, any help would be awesome.

Kamikaze
02-14-2011, 06:38:25 PM
Need to charge up your battery first then do a load test on it to verify it's condition is still good and will accept a charge.

If it has dead cells, and won't accept a charge, you may have already had a good working alternator but also a bad battery

Bikefixr
02-14-2011, 09:32:10 PM
Is it a single-wire type alternator? If so, you have to excite the Diodes by revving to about 2000 RPM. If it's astock type, then you need to make sure the alternator actully turns on. The big red wire goes to the starter and eventually tot he battery. The plug that sticks intot he alt case has 2 wires in it. One of them is keyed 12v and that tells the alternator to turn on. If you have a bad plug, or broken wire, the alt will spin but do nothing.

crome dome
02-14-2011, 11:18:39 PM
Wasn't there also a topic awhile back about not having the charging dummy light in the instrument panel and that could cause the alternator to not turn on. Seems I remember this being a problem for some folks after they installed aftermarket guages.

Cardinal
02-14-2011, 11:51:14 PM
Wasn't there also a topic awhile back about not having the charging dummy light in the instrument panel and that could cause the alternator to not turn on. Seems I remember this being a problem for some folks after they installed aftermarket guages.

+1 for "alternator idiot lamp" burned out. I had a 80 Monza 2+2 that drove me nuts when the alternator wouldn't charge! Finally a friend of mine told me to change the alternator idiot light. Alternator started charging.

Andelin74
02-15-2011, 12:36:13 AM
Is it a single-wire type alternator? If so, you have to excite the Diodes by revving to about 2000 RPM. If it's astock type, then you need to make sure the alternator actully turns on. The big red wire goes to the starter and eventually tot he battery. The plug that sticks intot he alt case has 2 wires in it. One of them is keyed 12v and that tells the alternator to turn on. If you have a bad plug, or broken wire, the alt will spin but do nothing.


You just triggered a light bulb. I actually just removed the stock instrument cluster completely from the harness about 2 months ago. And i did notice that the alternator was only using 1 wire from the harness slot, and that one was being jumped to the BAT terminal. So technically, I could just run a wire from the other post on that harness(the one that is meant to go to an indicator) to any accessory "key" wire and it should start the alternator up right?

Fbird
02-18-2011, 04:21:31 PM
yup. here is the simplist diagram i have (hope it posts)
11938

mrvedit
02-18-2011, 06:24:03 PM
IIRC the "activate" line to the alternator needs to go through the idiot light or a resistor (around 100-400 ohms) or the alternator, depending on the model, might burn out.

Andelin74
02-19-2011, 02:34:03 AM
Thanks guys, installed a new dummy light wired to a keyed wire and it fired right up!

crome dome
02-20-2011, 12:49:16 AM
Thanks guys, installed a new dummy light wired to a keyed wire and it fired right up!
Good job. Does your car still have the factory guages. I still have to figure out where to add a bulb or resistor since I removed all the factory guages and lamps.

Andelin74
02-20-2011, 04:58:04 AM
Good job. Does your car still have the factory guages. I still have to figure out where to add a bulb or resistor since I removed all the factory guages and lamps.

No i took out the stock cluster completely and i have a sheet metal aluminum dash with custom gauges and toggles. I just installed a bulb on my dash and wired it to the original dummy light wires from the harness.

crome dome
02-20-2011, 11:12:44 AM
Cool, Thanks.